Not Applicable
Not Applicable
This invention relates generally to flow meter calibration and proving devices, and more specifically to a magnetically coupled, positive displacement, small volume, multi-axial, isokinetic, device that can be used as a flow calibrator or prover.
Flow calibrators or provers are used by metrology labs, flow sensor manufacturers, and field calibration operators. For users calibrating flow sensors requiring high accuracy, variable flow rates, extended flow turndowns, various calibrating fluids, and in some cases, fluctuating process conditions, the industry standard, positive displacement type calibrators/provers traditionally employed are: (1) The xe2x80x9cspherexe2x80x9d calibrator/prover, often referred to as xe2x80x9cballxe2x80x9d or xe2x80x9cpipexe2x80x9d calibrator/provers, (2) The oscillating piston calibrator/prover, and (3) The xe2x80x9csmall volumexe2x80x9d calibrator/prover (SVP). For custody transfer installations, these devices must provide an uncertainty of 1 part out of 10,000, as mandated in API Chapter 4, Manual of Petroleum Measurement Standards.
1) The xe2x80x9cspherexe2x80x9d calibrator/prover typically uses over-inflated, spherical, elastomeric displacers, and requires large volumes of displaced calibration fluid per operation, due to the inherent repeatability inaccuracy of the mechanically activated, volume detector switches employed therein. They may be operated in a uni-, or bi-directional mode. They are typically constructed of commercial grade, carbon steel, pipe and fittings.
2) The oscillating piston type of calibrator/prover typically employs a solid metal, free floating piston, with xe2x80x9ccupxe2x80x9d seals, that oscillate between detector switches and is similar to the xe2x80x9cspherexe2x80x9d type, in construction, and large volume displacement required.
3) The SVP type of calibrator/prover typically utilizes an internal metal poppet valve mounted in a precision machined steel piston, with special seals, oscillating in a plated, honed, precision machined, cylindrical flow tube. The piston is retracted upstream between calibration cycles by means of a pneumatic, hydraulic, or mechanical coupling of the piston shaft. The displaced volume of the SVP is a fraction of that for the xe2x80x9cspherexe2x80x9d or oscillating piston types due to the use of precision volume detector switches, dual megahertz chronometers, and pulse interpolation of the test sensor""s output. The requirements for the SVP, are defined in the API, Manual of Petroleum Measurement Standards, Chapters 4.3, and 4.6.
The moderate to high cost of xe2x80x9cspherexe2x80x9d, oscillating piston, and SVP type calibrator/provers, typically restricts the use of these devices to those users, and service contractors, involved in custody transfer of hydrocarbon liquids, manufacturers of large quantities of flow sensors, and commercial metrology facilities. Start/stop operation of the displacer is common to all of these devices. Other inherent disadvantages are:
1) xe2x80x9cSpherexe2x80x9d and oscillating piston types require a large amount of dedicated, cubic operating space, and high volume storage tanks for calibrating fluids, in the calibration lab. Cost of ownership is considerable, including maintenance and periodical NIST traceable recertification. The use of various calibrating fluids is restricted by the materials of construction of the device. Due to large dispensed volumes required, multi-pass calibrations, which require start/stop of the displacer, and those performed at low flow rates can be extraordinarily lengthy.
2) SVP types achieve the industry mandated accuracy, with the use of precision electronics, pulse interpolation, and special proprietary seals, operating in a precision honed cylinder. The cylinder is typically centrifugally cast or forged. Care must be exercised to prevent these surfaces from corrosion and minute defects. Energy and time must be expended to retract the oscillating piston upstream, against the fluid flow, between calibration cycles. Another inherent disadvantage of the SVP, is the inability to accurately calibrate flow sensors with minimal or irregular pulse counts per unit of displaced volume, due to the small amount of displaced fluid per calibration cycle. Also, mass flow meters such as the coriolis type not only require larger amounts of displaced fluid per cycle, but are affected by the flow perturbations induced when the poppet valve closes to launch the piston downstream. When the SVP is equipped with the typical up and downstream volume switches, the dispensed volume represented by the spacing of these two switches must also be displaced through small flow sensors that could be calibrated with much less volume displaced. Cost of ownership is typically less than that for xe2x80x9cspherexe2x80x9d types, but still considerable.
A primary object of the present invention is to provide a magnetically coupled, small volume, positive displacement, fully automatic, flow sensor calibrator/prover.
Another object of the invention is to provide a high accuracy, economical calibrator/prover, with increased operating speed, that requires minimally dispensed calibration fluid, and a small operating space, without precision machined, proprietary components.
Yet another object of the invention is to perform single or multi-pass, calibration cycles by isokinetically dispensing increments of the composite volume displaced during a single, unidirectional transit of the displacer.
In accordance with a preferred embodiment of the present invention, xe2x80x98The invention includes a single, or multiple serially connected, flow tube(s), the number of which determines the number of calibration cycles performed, with one unidirectional passage of a free floating displacer, from initiation to acquisition in an Inline Automatic Launch/Retrieve Station (LRS), means a discrete, pre-calibrated, displaced volume of calibration fluid for each flow tube, equating to spacing between Volume Detector Sensors (VDS), is isokinetically dispensed by the displacer through test meters(s), while simultaneously, the electronic outputs from the VDS, the test meter(s), and optional auxiliary instruments, are interpolated, and processed in the P.C. or PLC based operator Monitoring and Control Station(MCS), means a cylindrical, convoluted, magnetically coupled displacer, with anti-compression device(s), and imbedded magnet(s), which emits an omni-directional magnetic field, is sequentially coupled to, and decoupled from, a coaxial, or parallel, oscillating, Volume Detector Actuator (VDA), means the calibration fluid flow propels the displacer, in one direction, through a flow tube, then a return bend, and subsequently through the next flow tube, in the opposite direction, reacquiring the outer ring of the VDA, to initiate the calibration cycle for that flow tube, means each outer ring of the VDA, is located concentrically,or parallel, to a flow tube, and is connected to a common, circular center ring, simultaneously oscillating with the outer ring(s), and traversing coaxial to a centrally mounted Volume Detector Rod (VDR), said VDA center ring sequentially activates the VDS""s, by means of a VDS Initiator, a projection integral to the VDA, and maintains dynamic concentricity by virtue of integral centering devices located in the VDA center ring.
The inclusion of a convoluted, cylindrical displacer in the apparatus, in lieu of the spherical type previously employed, allows the displacer to traverse pipeline tees, and standard, long radius elbows. The omni-directional imbedded magnet (s), enables the displacer to magnetically couple to, and decouple from, a coaxial, or parallel, oscillating, VDA. The convolutions of the displacer provide multiple, dynamic, seal surfaces, separated by liquid filled annular spaces, and eliminates inner poppet seals of the xe2x80x9csmall volumexe2x80x9d piston type prover(SVP). This combination of elements eliminates the start/stop operation of previous designs, and provides multiple, sequential, calibration cycles, for multiple sensors, with a single, unidirectional, passage of the displacer, the number of calibration cycles defined by the number of serially connected flow tubes.
The apparatus can provide multiple calibration cycles during the continuous, unidirectional passage of the displacer, the number of cycles, and volume dispensed, defined by the number of coaxial, or parallel, serially connected, flow tubes, thereby eliminating flow perturbations. Multiple flow sensors can be calibrated, simultaneously, and flow rates can be constant or modulated. The operator can configure the dynamic flow rate control as required. For custody transfer proving operations, wherein the repeatability of the flow sensor is established, the apparatus provides the required multiple calibration cycles, without a start/stop oscillation of the displacer, with a single, continuous, unidirectional, isokinetically dispensing, passage of the displacer, from launch to retrieve.